Conventionally, an FED device is operated by a vacuum microelectronic technique which is based on an electron transmission in a vacuum condition. Since the FED device employs an FED phenomenon by a quantum dynamic tunneling, less electricity is consumed. The emitted current, which flows in a vacuum from a cathode, reaches up to tens of cm.sup.2, and the size of the FED device is only several .mu.m. Such a relationship allows a mass production using a semiconductor fabrication process and an integration with an electronic circuit.
FIG. 1 is a longitudinal cross-sectional view showing a cell, which is a main unit in a general FED device. As shown in this view, a plurality of columns of cathodes 2, which emits electrons, are arranged on a glass substrate 1. At the upper part of each cathode 2, micro tips 2a, each having a conical shape, are formed at a regular interval. When the cathode 2 is supplied with power, an electron beam is emitted upwardly from the points of each micro tip 2a in the vertical direction.
Gates 3 are arranged in an array to intersect with the cathodes 2 between each micro tip 2a of the cathodes 2. Insulating layers 4 are disposed between the cathodes 2 and the gates 3 at the intersecting sections thereof so that the cathodes 2 and the gates 3 are separated from each other. The gate 3 formed on the insulating layer 4 prevents an electron beam emitted from the point of the micro tip 2a from being diffused or being curved, and allows a regular and constant electron beam to go in the upper vertical direction. On the upper part of the gate 3, a spacer 5 is formed to surround a cell area, and has an opening in its center.
A fluorescent body 6, having a planar construction and a fluorescent material, is formed on the spacer 5 so as to cover the opening part of the spacer 5. An electron beam emitted from the micro tip 2a collides with the fluorescent body 6, causing the fluorescent material to become excited and emit light by fluorescence. On the fluorescent body 6 is formed a transparent anode 7 having a planar construction, which is capable of transmitting light and inducing electrons to flow to the fluorescent body 6 by generating an electric field. The anode 7 is entirely covered with a glass substrate 8.
FIGS. 2A through 2C are cross-sectional views showing the fabrication method for a micro tip according to a conventional art. First, as shown in FIG. 2A, an oxide film 13 is formed by a oxidation process on an n-type or a p-type silicon substrate 11. Next, as shown in FIG. 2B, an oxide film pattern related to the region for the formation of the micro tip 12 is formed on the oxide film by a photo etching process, and the substrate 11 is etched using the oxide film pattern as a mask.
The wet-etching of the substrate 11 is carried out with a solution including Potassium Hydroxide (KOH) as a base, and Hydrogen Peroxide (H.sub.2 O.sub.2) and Isopropyl Alcohol (CH.sub.3 CHOHCH.sub.3) mixed therewith. In this wet-etching process, the conical shape of the micro tip 12 is fabricated by using as a mask the oxide film 13 patterned by the photo etching process, employing an anisotropic etching characteristic of the above etching solutions, and controlling a concentration of the etching solutions and an etching time. The fabrication process is completed by stripping the oxide film 13 which remains on the points of the micro tips 12, by an etching process using Hydrogen Fluoride (HF).
The above-mentioned fabrication method of the conventional micro tip 12 includes forming the oxide film 13 on the silicon substrate 11, forming a pattern on the oxide film 13 by a photo etching process, forming a shape of the micro tip 12 by etching the silicon substrate 11 on which the oxide film 13 is formed with an etching solution having an anisotropic etching characteristic, and stripping the oxide film 13 which remains on the points of the micro tips 12.
The conventional micro tip fabricated by the above described steps is disadvantageous since the micro tip cannot be formed with a desired conical shape. For example, a central axis of a conical-shaped tip is not formed as a straight line, or a shape of the tip is formed as a polygon, not as a precise conical shape. In addition, since the height of each tip is formed irregularly and the distribution of the electric field is not regular, a screen image, in which an FED device is employed, is not formed clearly. As a result, the durability of the FED device is shortened, and it is difficult to control an etching ratio for forming a desirable shape of a micro tip.